/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.protobuf;

import org.apache.yetus.audience.InterfaceAudience;

/**
 * Protobufs utility.
 */
@InterfaceAudience.Private
public class ProtobufMagic {

    private ProtobufMagic() {
    }

    /**
     * Magic we put ahead of a serialized protobuf message.
     * For example, all znode content is protobuf messages with the below magic
     * for preamble.
     */
    public static final byte[] PB_MAGIC = new byte[]{'P', 'B', 'U', 'F'};

    /**
     * @param bytes Bytes to check.
     * @return True if passed <code>bytes</code> has {@link #PB_MAGIC} for a prefix.
     */
    public static boolean isPBMagicPrefix(final byte[] bytes) {
        if(bytes == null)
            return false;
        return isPBMagicPrefix(bytes, 0, bytes.length);
    }

    /*
     * Copied from Bytes.java to here
     * hbase-common now depends on hbase-protocol
     * Referencing Bytes.java directly would create circular dependency
     */
    private static int compareTo(byte[] buffer1, int offset1, int length1, byte[] buffer2, int offset2, int length2) {
        // Short circuit equal case
        if(buffer1 == buffer2 && offset1 == offset2 && length1 == length2) {
            return 0;
        }
        // Bring WritableComparator code local
        int end1 = offset1 + length1;
        int end2 = offset2 + length2;
        for(int i = offset1, j = offset2; i < end1 && j < end2; i++, j++) {
            int a = (buffer1[i] & 0xff);
            int b = (buffer2[j] & 0xff);
            if(a != b) {
                return a - b;
            }
        }
        return length1 - length2;
    }

    /**
     * @param bytes Bytes to check.
     * @param offset offset to start at
     * @param len length to use
     * @return True if passed <code>bytes</code> has {@link #PB_MAGIC} for a prefix.
     */
    public static boolean isPBMagicPrefix(final byte[] bytes, int offset, int len) {
        if(bytes == null || len < PB_MAGIC.length)
            return false;
        return compareTo(PB_MAGIC, 0, PB_MAGIC.length, bytes, offset, PB_MAGIC.length) == 0;
    }

    /**
     * @return Length of {@link #PB_MAGIC}
     */
    public static int lengthOfPBMagic() {
        return PB_MAGIC.length;
    }
}
